This invention relates to an X-ray generator having a first high-voltage source and an X-ray tube which is provided with an anode, a first cathode and a second cathode which is electrically independent from the first cathode. A first high voltage supplied by the first high-voltage source is applied to a first system formed by the anode and the first cathode to obtain a first X-ray radiation. Further, the X-ray generator includes a second high-voltage source which delivers a high voltage different from the first high voltage.
Current X-ray apparatus used in security systems for examining freight and packages, are capable of distinguishing materials from one another, in addition to producing a shadow image of the contents. For such an operation the object under examination has to be irradiated with X-ray beams having two different discreet energy levels or energy level ranges. According to a technical solution, two sequential fan-shaped X-ray beams are generated which consecutively pass through the object. The energy levels of the fan-shaped beams are different, and thus a comparison of the spectra to be examined and derived from the object leads to a material classification.
For effecting a classification of material, it is known to arrange mechanically side-by-side two X-ray tubes for X-ray generators having different limit energy levels. For reasons of mechanical and high-voltage technology such X-ray generators require a certain minimum volume, and therefore the distance between the two fan-shaped beams has a minimum limit value which cannot be reduced. Such a circumstance, however, leads to technological disadvantages, particularly caused by mechanical tolerances, drifts in temperature and wear which lead to erroneous measuring data and thus adversely affect the accuracy of the measuring system.
German Patent No. 3,635,395 discloses an X-ray generator for producing at least two different X-ray radiations. The X-ray tube of the generator has at least two mutually independent cathodes which cooperate with an anode at different high voltages. Two or more X-ray beams are generated at different locations on a side of the anode.
German Offenlegungsschrift (application published without examination) No. 31 39 899 discloses an X-ray tube having two annular anodes and a cathode arrangement which encircles the anodes. In the annular anodes an opening is provided into or between which the material to the examined may be introduced.